When the price of bitcoins fell back from $20 in July 2011 lots of people turned off their miners, and so the difficulty fell. Anytime there is less hashing power in the preceding two weeks the difficulty will fall. The reverse is also true and once the first batch of ASIC's ships then yes, the difficulty will rise by a significant amount.
I would like to check if I get it right, after the ASICs will be realesed , the difficulty will go up really fast, am I right?
And why is that sometimes the difficulty drops?